Interactions of dendritic cells with fibronectin and endothelial cells

In Vitro Blood-Brain Barrier Models for Neuroinfectious Diseases: A Narrative Review

The blood-brain barrier (BBB) is a complex, dynamic, and adaptable barrier between the peripheral blood system and the central nervous system. While this barrier protects the brain and spinal cord from inflammation and infection, it prevents most drugs from reaching the brain tissue. With the expanding interest in the pathophysiology of BBB, the development of in vitro BBB models has dramatically evolved. However, due to the lack of a standard model, a range of experimental protocols, BBB-phenotype markers, and permeability flux markers was utilized to construct in vitro BBB models. Several neuroinfectious diseases are associated with BBB dysfunction. To conduct neuroinfectious disease research effectively, there stems a need to design representative in vitro human BBB models that mimic the BBB's functional and molecular properties. The highest necessity is for an in vitro standardised BBB model that accurately represents all the complexities of an intact brain barrier. Thus, this in-depth review aims to describe the optimization and validation parameters for building BBB models and to discuss previous research on neuroinfectious diseases that have utilized in vitro BBB models. The findings in this review may serve as a basis for more efficient optimisation, validation, and maintenance of a structurally- and functionally intact BBB model, particularly for future studies on neuroinfectious diseases.

Generating Bovine Monocyte-Derived Dendritic Cells for Experimental and Clinical Applications Using Commercially Available Serum-Free Medium

Advances in fundamental and applied immunology research often originate from pilot studies utilizing animal models. While cattle represent an ideal model for disease pathogenesis and vaccinology research for a number of human disease, optimized bovine culture models have yet to be fully established. Monocyte-derived dendritic cells (MoDC) are critical in activating adaptive immunity and are an attractive subset for experimental and clinical applications. The use of serum-supplemented culture medium in this ex vivo approach is undesirable as serum contains unknown quantities of immune-modulating components and may induce unwanted immune responses if not autologous. Here, we describe a standardized protocol for generating bovine MoDC in serum-free medium (AIM-V) and detail the MoDC phenotype, cytokine profile, and metabolic signature achieved using this culture methodology. MoDC generated from adult, barren cattle were used for a series of experiments that evaluated the following culture conditions: medium type, method of monocyte enrichment, culture duration, and concentration of differentiation additives. Viability and yield were assessed using flow cytometric propidium iodide staining and manual hemocytometer counting, respectively. MoDC phenotype and T cell activation and proliferation were assessed by flow cytometric analysis of surface markers (MHC class II, CD86, CD14, and CD205), and CD25 and CFSE respectively. Cytokine secretion was quantified using a multiplex bovine cytokine panel (IL-1α, IL-1β, IL-8, IL-10, IL-17A, IFN-γ, MIP-1α, TNF-α, and IL-4). Changes in cell metabolism following stimulation were analyzed using an Extracellular Flux (XFe96) Seahorse Analyzer. Data were analyzed using paired t-tests and repeated measures ANOVA. Immature MoDC generated in serum-free medium using magnetic-activated cell sorting with plate adhesion to enrich monocytes and cultured for 4 days have the following phenotypic profile: MHC class II⁺⁺⁺, CD86⁺, CD205⁺⁺, and CD14^-. These MoDC can be matured with PMA and ionomycin as noted by increased CD86 and CD40 expression, increased cytokine secretion (IL-1α, IL-10, MIP-1α, and IL-17A), a metabolic switch to aerobic glycolysis, and induction of T cell activation and proliferation following maturation. Cultivation of bovine MoDC utilizing our well-defined culture protocol offers a serum-free approach to mechanistically investigate mechanisms of diseases and the safety and efficacy of novel therapeutics for both humans and cattle alike.

Enriched Cd141+ DCs in the joint are transcriptionally distinct, activated, and contribute to joint pathogenesis

CD141+ DC are implicated in antiviral and antitumor immunity. However, mechanistic studies in autoimmune disease are limited. This is the first study to our knowledge examining CD141+ DC in autoimmune disease, specifically inflammatory arthritis (IA). We identified significant enrichment of CD141+ DC in the inflamed synovial joint, which were transcriptionally distinct from IA and healthy control (HC) blood CD141+ DC and significantly more activated, and they exhibited increased responsiveness to TLR3. Synovial CD141+ DC represent a bone fide CD141+ DC population that is distinct from CD1c+ DC. Synovial CD141+ DC induced higher levels of CD4+ and CD8+ T cell activation compared with their peripheral blood counterparts, as made evident by expression of IFN-γ, TNF-α, and granulocyte-macrophage CSF (GMCSF). Autologous synovial CD141+ DC cocultures also induce higher levels of these cytokines, further highlighting their contribution to synovial inflammation. Synovial CD141+ DC-T cell interactions had the ability to further activate synovial fibroblasts, inducing adhesive and invasive pathogenic mechanisms. Furthermore, we identify a mechanism in which synovial CD141+ DC are activated, via ligation of the hypoxia-inducible immune-amplification receptor TREM-1, which increased synovial CD141+ DC activation, migratory capacity, and proinflammatory cytokines. Thus, synovial CD141+ DC display unique mechanistic and transcriptomic signatures, which are distinguishable from blood CD141+ DC and can contribute to synovial joint inflammation.

Poly(Lactic Acid) Nanoparticles Targeting α5β1 Integrin as Vaccine Delivery Vehicle, a Prospective Study

Biodegradable polymeric nanoparticles are vehicles of choice for drug delivery and have the ability to encapsulate and present at their surface different molecules of interest. Among these bio-nanocarriers, poly(lactic acid) (PLA) nanoparticles have been used as adjuvant and vehicle for enhanced vaccine efficacy. In order to develop an approach to efficient vaccine delivery, we developed nanoparticles to target α5β1 positive cells. We first overproduced, in bacteria, human fibronectin FNIII9/10 recombinant proteins possessing an integrin α5β1 binding site, the RGDS sequence, or a mutated form of this site. After having confirmed the integrin binding properties of these recombinant proteins in cell culture assays, we were able to formulate PLA nanoparticles with these FNIII9/10 proteins at their surface. We then confirmed, by fluorescence and confocal microscopy, an enhanced cellular uptake by α5β1+ cells of RGDS-FNIII9/10 coated PLA nanoparticles, in comparison to KGES-FNIII9/10 coated or non-coated controls. As a first vaccination approach, we prepared PLA nanoparticles co-coated with p24 (an HIV antigen), and RGDS- or KGES-FNIII9/10 proteins, followed by subcutaneous vaccine administration, in mice. Although we did not detect improvements in the apparent humoral response to p24 antigen in the serum of RGDS/p24 nanoparticle-treated mice, the presence of the FNIII proteins increased significantly the avidity index of anti-p24 antibodies compared to p24-nanoparticle-injected control mice. Future developments of this innovative targeted vaccine are discussed.

Serum endostatin levels are elevated in colorectal cancer and correlate with invasion and systemic inflammatory markers

Background:

Endostatin, a fragment of collagen XVIII, is an endogenous angiogenesis inhibitor with anti-tumour functions. However, elevated circulating endostatin concentrations have been found in several human cancers including colorectal cancer (CRC).

Methods:

Serum endostatin levels were measured by enzyme-linked immunoassay from a series of 143 patients with CRC and from 84 controls, and correlated with detailed clinicopathological features of CRC, serum leukocyte differential count and C-reactive protein (CRP) levels.

Results:

Patients with CRC had higher serum endostatin levels than the controls (P=0.005), and high levels associated with age, tumour invasion through the muscularis propria and poor differentiation, but not with metastases. Endostatin levels showed a positive correlation with the markers of systemic inflammatory response and a negative correlation with the densities of tumour-infiltrating mast cells and dendritic cells. Collagen XVIII was expressed in tumour stroma most strikingly in blood vessels and capillaries, and in the muscle layer of the bowel wall.

Conclusions:

Elevated endostatin levels in CRC correlate with systemic inflammation and invasion through the muscularis propria. Increased endostatin level may be a result of invasion-related cleavage of collagen XVIII expressed in the bowel wall. The negative correlations between serum endostatin and intratumoural mast cells and immature dendritic cells may reflect angiogenesis inhibition by endostatin.

Generation and functional analysis of human TNF-α/iNOS-producing dendritic cells (Tip-DC)

BACKGROUND

A unique type of CD11c(pos) dendritic cells (DC) is abundant in inflamed tissue, for example, in chronic inflammatory skin diseases. Due to their remarkable production of tumor necrosis factor (TNF)-α and inducible NO synthase (iNOS), these cells have been referred to as TNF and iNOS-producing DC (Tip-DC). While Tip-DC have been mainly characterized in murine models of infection, functional data about their human counterpart are lacking.

OBJECTIVES

We sought to generate human Tip-DC in vitro und thus provide a new model for the investigation of their phenotype and function.

METHODS

We generated human Tip-DC from monocytic precursor cells of healthy individuals, atopic and psoriatic patients using human serum. Resting and stimulated cells were analyzed by flow cytometry, real-time PCR, and by ELISA. INOS activity was measured by fluorometric detection of NO.

RESULTS

Tip-DC closely resembled their in vivo counterparts by expressing CD11c, CD86, and CD40 while lacking CD1a, CD1c, or CD207/Langerin. Bacterial stimulation of Tip-DC from healthy donors, atopic dermatitis, or psoriasis patients resulted in a similar increase in iNOS activity and TNF-α production. In kinetic experiments, TNF-α, a putative activator of Tip-DC, could not induce NOS2. Upon bacterial stimulation, TNFA, IL6, IL12B, and IL23A mRNA appeared in a first wave, while IL12A and NOS2 mRNA were up-regulated later on but not blocked by anti-TNF-α agents, implying a biphasic pro-inflammatory response.

CONCLUSIONS

We developed a new model for the study of human Tip-DC and provide the first evidence of their pro-inflammatory capacity.

Astrocytes inhibit microglial surface expression of dendritic cell-related co-stimulatory molecules through a contact-mediated process

Murine microglia cultured in isolation were treated sequentially with granulocyte/monocyte colony-stimulating factor (GM-CSF) (5 days) and lipopolysaccharide (LPS) (2 days) to elicit a mature dendritic cell-like (DC-like) phenotype. Examined by flow cytometry microglia thus isolated show high surface expression of CD11c together with the co-stimulatory molecules CD40, CD80, and CD86 that are necessary for T-cell activation. In contrast, microglia co-cultured with astrocytes fail to achieve a mature DC-like phenotype. Contact with the astrocytic environment is necessary for the inhibition. Failure was not because of a more rapid degradation of protein. Bone marrow-derived cells, like microglia, were prevented by astrocytes from attaining a mature DC phenotype. Although GM-CSF pre-treatment substantially increases mRNA of co-stimulatory molecules and major histocompatibility complex (MHC) Class II in isolated microglia, co-cultured microglia await treatment with LPS to up-regulate them. In contrast, western blot and immunocytochemical analysis revealed that it is not a failure of transcription or translation, nor is it a more rapid degradation of mRNA that is responsible for the low surface expression; rather microglia co-cultured with astrocytes produce mRNA and protein but do not traffic the protein onto the cell surface.

Development of a three-dimensional, all-human in vitro model of the blood-brain barrier using mono-, co-, and tri-cultivation Transwell models

In vitro models of the blood-brain barrier (B-BB) generally utilise murine or porcine brain endothelium and rat astrocytes which are commonly grown in foetal calf serum supplemented conditions which modulate cell growth rates. Consequently, results gained from these experimental models can be difficult to extrapolate to the human in vivo situation since they are not of human origin. The proposed in vitro Transwell model of the B-BB is a multi-culture human cell system. It requires reconstruction of the human derived B-BB components in vitro (cerebral microvascular endothelial cells, astrocytes, and brain vascular pericytes) in a three-dimensional (3D) configuration based on Transwell filters. Different cell permutations (mono-, co-, and tri-cultivation) were investigated to find the most effective model in terms of tight junction resistance of the human cerebral microvascular endothelial cells. The B-BB model permutations comprised of human astrocytes (CC-2565 and SC-1810), human brain vascular pericytes (HBVP), and human cerebral microvascular endothelial cells (hCMEC/D3), under human serum supplementation. The models were assessed by trans-endothelial electrical resistance (TEER) measurements using an epithelial voltohmmeter, to validate the tight junction formation between hCMEC/D3 cells. Mono-, co-, and tri-cultivation Transwell models constructed with human brain-derived cells under human serum supplementation demonstrated that co-cultivation of astrocytes with endothelial cells produced the most successful model, as determined by TEER. Pericytes on the other hand improved tight junction formation when co-cultured with endothelial cells but did not improve the model to such an extent when grown in tri-cultivation with astrocytes.

Dendritic cell internalization of foot-and-mouth disease virus: influence of heparan sulfate binding on virus uptake and induction of the immune response

Dendritic cells (DC), which are essential for inducing and regulating immune defenses and responses, represent the critical target for vaccines against pathogens such as foot-and-mouth disease virus (FMDV). Although it is clear that FMDV enters epithelial cells via integrins, little is known about FMDV interaction with DC. Accordingly, DC internalization of FMDV antigen was analyzed by comparing vaccine virus dominated by heparan sulfate (HS)-binding variants with FMDV lacking HS-binding capacity. The internalization was most efficient with the HS-binding virus, employing diverse endocytic pathways. Moreover, internalization relied primarily on HS binding. Uptake of non-HS-binding virus by DC was considerably less efficient, so much so that it was often difficult to detect virus interacting with the DC. The HS-binding FMDV replicated in DC, albeit transiently, which was demonstrable by its sensitivity to cycloheximide treatment and the short duration of infectious virus production. There was no evidence that the non-HS-binding virus replicated in the DC. These observations on virus replication may be explained by the activities of viral RNA in the DC. When DC were transfected with infectious RNA, only 1% of the translated viral proteins were detected. Nevertheless, the transfected cells, and DC which had internalized live virus, did present antigen to lymphocytes, inducing an FMDV-specific immunoglobulin G response. These results demonstrate that DC internalization of FMDV is most efficient for vaccine virus with HS-binding capacity, but HS binding is not an exclusive requirement. Both non-HS-binding virus and infectious RNA interacting with DC induce specific immune responses, albeit less efficiently than HS-binding virus.

A new group B adenovirus receptor is expressed at high levels on human stem and tumor cells

CD46 is used by human group B adenoviruses (Ads) as a high-affinity attachment receptor. Here we show evidence that several group B Ads utilize an additional receptor for infection of human cells, which is different from CD46. We tentatively named this receptor receptor X. Competition studies with unlabeled and labeled Ads, recombinant Ad fiber knobs, and soluble CD46 and CD46 antibodies revealed three different subgroups of group B Ads, in terms of their receptor usage. Group I (Ad16, -21, -35, and -50) nearly exclusively uses CD46. Group II (Ad3, -7p, and -14) utilizes receptor X and not CD46. Group III (Ad11p) uses both CD46 and the alternative receptor X. Interaction of group II and III Ads with receptor X occurs via the fiber knob. Receptor X is an abundantly expressed glycoprotein that interacts with group II and III Ads at relatively low affinity in a Ca(2+)-dependent manner. This receptor is expressed at high levels on human mesenchymal and undifferentiated embryonic stem cells, as well as on human cancer cell lines. These findings have practical implications for stem cell and gene therapy.

A critical role for prostaglandin E2 in podosome dissolution and induction of high-speed migration during dendritic cell maturation

Dendritic cells (DCs) are professional APCs of the immune system that play a key role in regulating T cell-based immunity. The capacity of DCs to activate T cells depends on their maturation state as well as their ability to migrate to the T cell areas of draining lymph nodes. In this study, we investigated the effects of DC maturation stimuli on the actin cytoskeleton and beta(1) integrin-dependent adhesion and migration. Podosomes, specialized adhesion structures found in immature monocyte-derived DCs as well as myeloid DCs, rapidly dissolve in response to maturation stimuli such as TNF-alpha and PGE(2), whereas the TLR agonist LPS induces podosome dissolution only after a long lag time. We demonstrate that LPS-mediated podosome disassembly as well as the onset of high-speed DC migration are dependent on the production of PGs by the DCs. Moreover, both of these processes are inhibited by Ab-induced activation of beta(1) integrins. Together, these results show that maturation-induced podosome dissolution and loss of alpha(5)beta(1) integrin activity allow human DCs to undergo the transition from an adhesive to a highly migratory phenotype.

Evidence for an enhanced adhesion of DC to fibronectin and a role of CCL19 and CCL21 in the accumulation of DC around the pre-diabetic islets in NOD mice

The non-obese diabetic (NOD) mouse is a widely used animal model for the study of human diabetes. The lymphocytic (peri-)insulitis is preceded by an early accumulation of dendritic cells (DC) around the islets of Langerhans. This DC accumulation is thought to derive from an influx of monocytes attracted by pro-inflammatory chemokines. Besides chemokines, extracellular matrix (ECM) proteins play an important role in the accumulation of leukocytes in tissues. We studied the expression of the chemokines CCL2, CCL5, CXCL10, CCL19 and CCL21 over time in pancreases of NOD and control mice by ELISA on pancreas lysates as well as by immunohistochemistry. In addition, we studied the adhesive capacity of bone marrow-derived DC (BMDC) to ECM components. DC in the NOD pancreas accumulated at sites with an intense expression of fibronectin. In vitro, NOD BMDC showed increased fibronectin adhesion and increased VLA-5 expression. At the time of early DC accumulation (<10 wk), the lymphoid tissue-related chemokines CCL19 and CCL21 were increased. Our findings support the view that the early accumulation of DC around the NOD islets is not the consequence of an enhanced attraction of precursors and immature DC by pro-inflammatory chemokines. It rather might be the consequence of an aberrantly enhanced adhesion and retention of NOD DC.

CC chemokine receptor 4 ligand production by bronchoalveolar lavage fluid cells in cigarette-smoke-associated acute eosinophilic pneumonia

We examined the production of macrophage-derived chemokine (MDC/CCL22) and thymus- and activation-regulated chemokine (TARC/CCL17) by bronchoalveolar lavage fluid (BALF) cells in cigarette-smoke-associated acute eosinophilic pneumonia (CS-AEP). The CC Chemokine Receptor 4 (CCR4) ligand levels in BALF from patients with CS-AEP were considerably higher than those in healthy volunteers and correlated well with Th2 cytokine levels. Interleukin-4 enhanced CCR4 ligand production. MDC expression was observed in CD68-positive cells from patients with CS-AEP and in healthy control smokers. In contrast, TARC expression in CD68- or CD1a-positive cells was detected only in CS-AEP. An in vivo cigarette smoke challenge test induced increases in CCR4 ligands in the BALF and in the cultured supernatant of BALF adherent cells. These results suggest that alveolar macrophages and dendritic cells contribute to the pathogenesis of CS-AEP by generating CCR4 ligands, probably in response to cigarette smoke.

Migration of polymorphonuclear leucocytes is influenced by dendritic cells

Dendritic cells (DCs) are the most potent antigen-presenting cells and populate many tissues where they may participate in inflammatory reactions. The infiltration of polymorphonuclear leucocytes (PMNLs) into tissues is a prominent feature of inflammation. The mechanisms of PMNL recruitment depend on chemotactic factors and adhesion molecules expressed on endothelial cells. The aim of the present study was to determine whether DCs participate in the early recruitment of PMNLs. Dendritic cells derived from peripheral blood monocytes were used for this study. PMNLs incubated with culture supernatant (CS) from untreated or from tumour necrosis factor-alpha (TNF-alpha)-treated (1 hr, 100 U/ml, 37 degrees ) monocyte-derived DCs (moDCs) had increased surface expression of both CD11b and CD18. Moreover, both untreated and TNF-alpha-treated moDCs induced PMNL chemotaxis. By blocking CXCL8, CXCL5, CXCL7 and Pan GRO (CXCL1, CXCL2, CXCL3), we observed that CXCL8/interleukin-8 might be the chemokine that induced the PMNL chemotactic activity in the CS of untreated and TNF-alpha-treated moDC. Furthermore, we investigated the regulation of CXCL8 production in moDCs by adhesion molecule engagement. Our data demonstrated that CD31, CD18, CD29 and CD49d participated in the adhesion of immature moDCs to endothelium. Moreover, engagement of domains 1-3 of CD31, but not of CD29 or CD18, decreased the production of CXCL8 by immature but not mature moDCs (which display lower CD31 levels than immature moDCs). Overall, these results suggest that DCs not only trigger a specific immune response, but also the innate immune response by recruiting PMNLs. Furthermore, our results also suggest that CXCL8 production by immature DCs might be regulated by signalling through CD31 during their migration through the vascular endothelium.

Maturation of DC is associated with changes in motile characteristics and adherence

Migration of dendritic cells (DC) from sentinel sites to lymphoid tissue entails the initiation and coordination of a complex series of cytoskeletal rearrangements resulting in polarised protrusion, formation of new adhesion points, and detachment. Although many diverse receptor-ligand interactions stimulating DC maturation and migration have been identified, the changes that occur in the structure of the actin cytoskeleton during these processes have received little attention. When derived in vitro, immature DC floated in clumps, and upon addition of maturation stimuli such as lipopolysaccharide (LPS), they rapidly adhered, developed polarity, and assembled actin-rich structures known as podosomes at the leading edge of the cell. Podosome assembly was associated with the specific recruitment of beta2 integrins, which in the absence of the Wiskott Aldrich Syndrome protein (WASp), did not occur. As maturation progressed, normal DC once again became rounded and devoid of podosomes. This change in morphology was closely associated with a quantitatively reduced ability to adhere to fibronectin or ICAM-1-coated surfaces. In immature DC, failure to form podosomes or selective inhibition of the CD18 component of podosomes resulted in a similarly reduced ability to adhere to ICAM-1, indicating that podosomes, through CD18, are necessary for tight adhesion to this ligand. We, therefore, propose that podosomes provide an essential link between directional cell protrusion and achievement of DC translocation by establishing new dynamic anchor points at the front of the cell. The temporal regulation of podosome assembly during DC maturation also suggests that they may be most critical for early movement, perhaps during transmigration of lymphatic endothelium.

Adhesion capacity and integrin expression by dendritic-like cells generated from acute myeloid leukemia blasts by calcium ionophore treatment

OBJECTIVE

Dendritic cells (DC) play a key role in initiation of immune responses. In vitro modified acute myeloid leukemia (AML) blasts acquire certain specific features of DC and are suggested as a potential source of anti-leukemia vaccines. AML-DC have been characterized in terms of costimulatory molecule expression and cytokine production. In contrast, migratory capacity of AML-DC, which is a major attribute of DC required for their in vivo function, remains unknown. Here we present data on adhesion properties and profile of integrin expression of AML-DC.

MATERIALS AND METHODS

Blasts from nine patients were used to generate AML-DC by calcium ionophore treatment. Adhesion of AML-DC to the major components of the extracellular matrix and the profile of integrin expression was studied using flow cytometry.

RESULTS

Similar to their normal counterparts, calcium ionophore-induced AML-DC acquired the ability to bind to fibronectin and in 4 of 7 studied cases to bind to denatured collagen. Adhesion to native collagen remained unchanged during DC-type differentiation of AML blasts. AML-DC and DC obtained from monocytes of healthy donors expressed CD49d, CD49e, alphavbeta3, and alphavbeta5. However, AML-DC from 3 of 8 patients down-regulated CD49d, which plays an important role in cell-to-cell and cell-to-matrix interactions and normally is coexpressed with CD83.

CONCLUSION

The results provide further evidence that AML blasts can be induced to display functional properties characteristic for DC and may prove useful for in vivo delivery and presentation of tumor antigens to the immune system. Abnormal CD49d expression and variability in AML-DC adhesion to denatured collagen indicate that motility of AML-DC from individual patients may vary, and a customized approach is essential for evaluating leukemic cell feasibility for vaccine design.